1. Technical Field
The invention described in this application relates generally to power supplies, and more particularly to a new and improved system providing an uninterrupted source of alternating current.
2. Background Information
Interruptions in AC input power, including voltage level variations beyond predefined limits, often produce unacceptable equipment operation. For example, a glitch in AC power supplying a conventional personal computer may result in lost data and other computer malfunctioning. This may cause extreme inconvenience and expense and thus, a clean uninterrupted source of power is often desired.
Various types of backup power supplies exist for this purpose. One type, commonly called an off-line supply, utilizes a set of batteries driving an up-converter to provide an independent source of AC power. A mechanical or electrical switching arrangement transfers to the off-line supply if there is a failure in AC power, and thus operation of the equipment being powered can continue.
Although effective in many respects, the off-line supply has certain drawbacks that need to be overcome, most notably the switchover time involved. It may take on the order of five to ten milliseconds to switch over to the backup supply, and this time lag often results in malfunctioning of the equipment being powered. In addition, the switching arrangement often results in transients that tend to further induce malfunctioning. Consequently, it is desirable to have a new and improved backup system that overcomes these concerns.
Another type of backup power supply, commonly called an on-line supply, rectifies the AC power to provide a DC current, converts the DC current back to AC, and then transforms the AC to the voltage level required by the equipment being powered. A set of batteries connected through a diode switching arrangement to the input of the converter takes over if there is an AC power failure and thus, effects of the interruption are minimized.
Although switchover time is significantly reduced, the on-line supply has certain other drawbacks. For example, it typically utilizes an input transformer for reducing the input AC voltage so that the voltage level of the rectified current is the same as the battery voltage, a converter for converting the DC to AC, and an output transformer for increasing the voltage to the desired output level. Each of these components is usually somewhat large, inefficient, and relatively expensive. Consequently, it is desirable to have a new and improved system that overcomes these concerns also--one that is more effective that combines increased efficiency with decreased size and cost.